The death toll from a powerful storm which lashed Australia's east coast and left homes hanging over the edge of the sea rose to four Tuesday, with three people still missing.

Torrential rains caused flooding across New South Wales over the weekend, with three people dying after their vehicles were swept away in rising waters.

In Sydney, high winds and huge seas caused coastal erosion which washed away beachfront lawns and damaged homes.

The storm then swept south to Victoria and the island state of Tasmania, where one woman died after her house was inundated and where two other people are still missing after being swept away by floodwaters.

A third person, a swimmer who reportedly jumped into the huge swell at Sydney's Bondi Beach on Monday before getting into difficulty, is also missing.

"It's certainly disastrous, this is an extreme weather event, the worst flooding we've experienced in this state in 40 years and it's likely to get worse," Tasmanian Premier Will Hodgman said.

In New South Wales, where the rain has eased, waves which on the weekend punched holes into surfside buildings and in one case swept an in-ground swimming pool onto the beach, caused further damage.

In the northern Sydney suburb of Collaroy, up to 50 metres of the beach had been lost, coastal engineer Ian Turner told AFP, with officials concerned about the safety of seven waterfront homes.

"You could audibly hear some creaking and cracking sounds coming from a couple of the homes," Turner said after spending much of Monday evening monitoring the area.

Collaroy resident Tony Cargorski told the Australian Broadcasting Corporation he had lost another two metres from the back of his home overnight, with his verandah falling into the ocean.

"I want to come back and with all my heart, with all my soul, see that house intact. And we can resume our lives," he said, but admitted there would be "tough times ahead".

The Insurance Council of Australia said as of early Tuesday, insurers had received 14,500 claims across Queensland, New South Wales, Victoria and Tasmania, with estimated insured losses of Aus$56 million (US$41.6 million).